1. Description of the Invention
The present invention pertains to electric measuring equipment in general and in particular to an apparatus that finds the ratio of electrical signals and measuring equipment that uses this apparatus.
2. Related Art
Technology for measuring the ratio between two electrical signals, such as network analyzers, apparatuses for measuring circuit elements, devices for measuring transmission or equipment for measuring phase and amplitude, etc., is used for many purposes. In particular, this ratio is a vector ratio when the electrical signals are alternating-current signals.
By means of prior art, two electrical signals to be determined are measured by separate measuring means and the ratio is found from the measurements that have been obtained where low precision is acceptable for the ratio measurement. Many network analyzers (for instance, Agilent 8715A marketed by Agilent Technology (Tokyo)) use this method.
Nevertheless, the conversion coefficient of the measuring means, that is, the ratio of the quantity to be measured and the measurement (usually a complex number), generally do not agree with the theoretical value due to differences in properties between the two measuring means. An error due to the above difference readily increases with an increase in frequency of the electrical signals to be measured.
One method of eliminating this difference is calibration, as long as the measuring means is linear. One method that is generally used for the calibration of the voltage ratio is the method whereby the output of one signal source is divided in two with a resistance-type distributor and the respective outputs are measured as input of the measuring means and the same measurements serve as the reference. However, by means of methods that use two measuring means, it is difficult to maintain 0.05% stability in terms of the amplitude of the measurements with changes in temperature of xc2x110xc2x0 after calibration and stability of 0.03xc2x0 in terms of phase due to differences in the properties of the respective structural parts.
The method whereby the same measuring means are used with the help of time division is employed as the ultimate method for minimizing and stabilizing the difference between the conversion coefficients of these measuring means. For instance, the method of time division is used with equipment for measuring impedance (for instance, Agilent 4294A made by Agilent Technology), which is one of the apparatuses used to measure circuit components, because stability of 0.05% in terms of the amplitude of the measurements (absolute value) and 0.03xc2x0 or less in terms of phase is required.
The ratio meter of the prior art shown in FIG. 1 comprises switch means 9 for time-division multiplexing of input signals, terminal resistance 16 connected in series to the output side of this switch means, measuring means 100, and control and computation apparatus 30. Switch means 9 comprises input switches 6 and 8 connected to input terminals 2 and 4 and connections that include junctions 10 and 12. Junction 10 is also an input terminal of measuring means 100. Terminal resistance 16 is connected to junction 12.
Voltage U corresponding to the current that flows to the device under test is introduced to input terminal 2. On the other hand, voltage V that corresponds to the voltage applied to the device under test is introduced to input terminal 4.
Input switches 6 and 8 are in the first state, wherein input terminals 2 and 4 are exclusively connected to measuring apparatus 14 and terminal resistance 16, respectively, (as shown by the solid switch lead lines) in the first time interval. Here, measuring apparatus 14 measures voltage V and measurement u is stored in memory 22. Input terminal 4 terminates at terminal resistance 16.
Input switches 6 and 8 are in the second state, where input terminals 4 and 2 are exclusively connected to measuring apparatus 14 and terminal resistance 16, respectively, (as shown by the broken switch lead lines) in the next second time interval. Here, measuring apparatus 14 measures voltage V and measurement v is stored in memory 24. Input terminal 2 terminates at terminal resistance 16. Control and computation apparatus 30 obtains the operation timing of input switches 6 and 8, output switch 20, and other components, or accesses memories 22 and 24 in order to input measurements u and v and calculates their ratio v/u. The voltage ratio that is found from the corrected formula, which has been found during calibration of this ratio, is calculated.
In this case, even if the conversion coefficient of measuring means 100 changes with temperature, etc., for instance such that u and v become ku and kv, (kv)/(ku)=v/u then the ratio that is measured will not change. The hypothesis that the value of resistance R1 of input resistance (generally impedance, but resistance is used in the following discussion for purposes of clarity and understanding of the invention, and not as a limitation of the invention) of measuring apparatus 14 and the value of resistance R2 of terminal resistance 16 are equal must be valid in order to accurately calibrate and measure by this measuring method.
Nevertheless, it is difficult to keep R1 and R2 the same within a wide frequency range when the frequency of voltages U and V increases, and there are cases where input impedances looking into ratio measuring means 100 from input terminal 2 or 4 takes on different values, depending on the switching state. Therefore, voltage sources U and V changes and V/U itself also changes in accordance with the switch state.
The method has also been used whereby an attenuator is introduced in front of each of input terminals 2 and 4 so that the above-mentioned changes present in the connection state of the switches are attenuated. However, by means of this method, the undesirable effect often occurs wherein voltages U and V that are input to measuring means 100 are attenuated and their signal-to-noise ratio is reduced, resulting in a reduction in measurement precision.
The object of the present invention is an apparatus and a method for accurate calibration and stable measurement of the ratio of electrical signals without requiring an unnecessary attenuator, even if there is a difference in the input impedance.
Another object of the present invention is an apparatus for measuring electric components and a method of measuring electric components that uses these very stable ratio measurements.
The first apparatus for measuring the ratio of electrical signals pertaining to the present invention comprises a switch means that comprises a first input terminal that receives a first electrical signal, a second input terminal that receives a second electrical signal, and a first and a second output terminal, and that has a first state, wherein the first input terminal and the first output terminal are connected and the second input terminal and the second output terminal are connected, as well as a second state, wherein the first input terminal and the second output terminal are connected and the second input terminal and the first output terminal are connected; a first measuring means for measuring electrical signals received from the above-mentioned first output terminal having a first receiving terminal connected to the above-mentioned first output terminal; a second measuring means for measuring electrical signals received from the above-mentioned second output terminal having a second receiving terminal connected to the above-mentioned second output terminal; and a control and computation means, which is connected to the above-mentioned switch means and the above-mentioned first and second measuring means and receives the respective measurements of the above-mentioned electrical signals of the above-mentioned first and second measuring means with the above-mentioned switch means and the above-mentioned first and second state, respectively, and calculates the ratio to be measured related to the above-mentioned first and second electrical signals, which forms a bilinear equation with the ratio of the measurements of the above-mentioned electrical signals of the above-mentioned second measuring means to the measurements of the above-mentioned electrical signals of the above-mentioned first measuring means, from the value of the above-mentioned ratio under the above-mentioned first and second states.
By means of the above-mentioned structure, it is possible to accurately calculate the ratio to be measured without any effect during the measurements on the source that generates the ratio to be measured or any effect from changes due to drifting of the conversion coefficient of the first and second measuring means (or gain, i.e., the ratio of the measurements to the received electrical signals), etc., because the state of the switch means was held unchanged during measurement of the ratio.
The second apparatus for measuring the ratio of electrical signals pertaining to the present invention is an apparatus for measuring the ratio of electrical signals according to the first apparatus for measuring the ratio of electrical signals pertaining to the present invention, wherein the geometric mean of the values under the above-mentioned first and second states of the ratio of the measurements of the above-mentioned electrical signals becomes the above-mentioned ratio to be measured.
The calculations are thereby simplified when the ratio to be measured is the ratio between the first and second electrical signals and therefore, there is an advantage in terms of measuring speed and cost.
The third apparatus for measuring the ratio of electrical signals pertaining to the present invention is an apparatus for measuring the ratio of electrical signals according to the second apparatus for measuring electrical signals pertaining to the present invention, wherein the arithmetic mean of the values under the above-mentioned first and second states of the ratio of the measurements of the above-mentioned electrical signals becomes the above-mentioned ratio to be measured.
Calculations of the ratio to be measured can be completed with a further simplified calculation means by using the arithmetic mean as the above-mentioned ratio to be measured when the difference between the above-mentioned ratio of the measurements of electrical signals under the above-mentioned first and second states and the value of the ratios of the values under the above-mentioned first and second states is relatively small because of this type of structure.
The fourth apparatus for measuring the ratio of electrical signals pertaining to the present invention is an apparatus for measuring the ratio of electrical signals according to the first apparatus for measuring the ratio of electrical signals of the present invention, wherein the above-mentioned first and second electrical signals are alternating-current signals and the above-mentioned ratio to be measured is the vector ratio.
The relative amplitude and phase difference of some electrical signals to other electrical signals and the values related to these can be easily found as the vector ratio of alternating-current signals because of this type of structure. Moreover, [this type of structure] has an advantage in that accurate values can be presented for many purposes, such as circuit network analyzers, equipment for measuring circuit components, devices for measuring transmission volume, equipment for measuring phase and amplitude, devices for measuring physical amounts, etc.
The fifth apparatus for measuring the ratio of electrical signals pertaining to the present invention is an apparatus for measuring the ratio of electrical signals according to the fourth apparatus for measuring the ratio of electrical signals pertaining to the present invention, wherein the above-mentioned ratio to be measured is immittance of an electronic component.
Measurement of electric components, including calibration, is accurately performed and therefore, the precision and stability of apparatuses for measuring impedance and circuit network analyzers can be improved because of this type of structure.
The sixth apparatus for measuring the ratio of electrical signals pertaining to the present invention is an apparatus for measuring the ratio of electrical signals according to either the fourth or fifth apparatus for measuring the ratio of electrical signals pertaining to the present invention having a structure wherein heterodyne detection of the above-mentioned electrical signals is performed by the above-mentioned first and second measuring means prior to the above-mentioned measurement, further comprising a local generator means for generating local signals used in the above-mentioned detection.
The frequency bandwidth and the frequency upper limit of the electrical signals that will be measured can be enlarged [and raised] a step further with almost no increase in the difference in measurements of the ratio to be measured because of this type of structure.
The seventh apparatus for measuring electrical signals pertaining to the present invention is an apparatus according to any of the first through fifth apparatuses for measuring the ratio of electrical signals pertaining to the present invention, wherein at least one of the above-mentioned first and second electrical signals will be received by the above-mentioned switch means via an attenuator.
The effects during measurement on the generation source of the ratio to be measured are further minimized because of this type of structure.
The first apparatus for measuring electric components pertaining to the present invention comprises the above-mentioned fifth or six apparatus for measuring the ratio of electrical signals; a starting-signal source for generating starting electrical signals; a power-splitting means connected to the starting-signal source for the input of starting electrical signals and dividing [these signals] into excitation signals and the above-mentioned first electrical signals; and a bridge means, which is a directional bridge excited by the above-mentioned excitation signals comprising a measuring terminal for connection of the device under test to one side of the above-mentioned directional bridge and with which detection signals of the above-mentioned directional bridge are output from the same output terminal as the above-mentioned second electrical signals; wherein the above-mentioned ratio to be determined has a value related to immittance of the above-mentioned device under test. By employing this type of structure, the detection signal of the directional bridge are measured instead of current flowing through the device under test, and therefore, immittance can be measured over a broader band of higher frequency.
The first method of calibrating an apparatus for measuring electric components pertaining to the present invention is a method with which the above-mentioned first apparatus for measuring electric components is calibrated, comprising the steps of
changing in succession the above-mentioned device under test by 3 different known impedances while keeping the above-mentioned switch means under the above-mentioned first state and determining the first constant group of the above-mentioned bilinear equation from the ratio to the above-mentioned first and second measurements in accordance with the above-mentioned known impedance; and changing in succession the above-mentioned device under test by 3 different known impedances while keeping the above-mentioned switch means under the above-mentioned second state and determining the first constant group of the above-mentioned bilinear equation from the ratio to the above-mentioned first and second measurements in accordance with the above-mentioned known impedance.
Three-point calibration is conducted whereby the above-mentioned device under test is changed in succession by three different known impedances without changing the state of the switch means and therefore, calibration reliability is improved because calibration is performed by this type of method.
The first method of measuring the ratio of electrical signals pertaining to the present invention comprises measuring the first received electrical signals pertaining to the above-mentioned first electrical signals with said first measuring means to obtain a first measurement and measuring the second received electrical signals pertaining to the above-mentioned second electrical signals to obtain a second measurement; measuring the third received electrical signals pertaining to the above-mentioned first electrical signals with the above-mentioned second measuring means to obtain a third measurement and measuring the fourth received electrical signals pertaining to the above-mentioned second electrical signals with the above-mentioned first measuring means to obtain a fourth measurement; and calculating the above-mentioned ratio to be measured pertaining to the ratio of the above-mentioned first and second measurements and the ratio of the above-mentioned third and forth measurements, wherein a measurement is obtained for a ratio to be measured, which forms a bilinear equation with the ratio of the first and second electrical signals exclusively input to the respective first and second measuring means connected to the respective first and second output terminals of a switch means that comprises a first input terminal that receives first electrical signals, a second input terminal that receives second electrical signals, and a first and second output terminal, and that has a first state, wherein the first input terminal and the first output terminal are connected and the second input terminal and the second output terminal are connected, as well as a second state, wherein the first input terminal and the second output terminal are connected and the second input terminal and the first output terminal are connected.
The switch means is kept under a constant state during measurement of the ratio and therefore accurate calculation of the ratio to be measured is possible without any effect during measurement on the generation source of the ratio to be measured and without any effect from changes due to drifting etc., of the conversion coefficient of the first and second measuring means (or gain, i.e., the ratio of the measurement to the received electrical signals), because this type of method is adopted.
Other embodiments of the present invention and their results will become obvious from the following description of the present specification.